Blood gas analyzers have become a widely used tool for clinical decision making. Essentially, a blood gas analyzer will measure the gas tension (partial pressure) in a given blood sample taken from a patient. For example, the amount of oxygen and carbon dioxide in a given blood sample might be respectively fifteen percent and seven percent. Analysis of such sample by the blood gas analyzer will reveal these values.
Because of protein contamination, electrode drift or simply plain human error, gas analyzers can become out-of-calibration and thus provide incorrect data. As a consequence, it is extremely important aside from legal liability considerations, for laboratory workers and the like to frequently check the blood gas analyzers and calibrate the same where necessary with quality control solutions.
With respect to the foregoing, it is known to provide ampules of blood or blood plasma or equivalent buffer solutions with known quantities of gas or gases such as oxygen and carbon dioxide, which can be broken open and used for quality control of the blood gas analyzer. However, these prepared solutions are relatively expensive. As a consequence, it has become the present day practice for various laboratories to use equilibrating instruments often referred to as tonometers for preparing quality control solutions as needed and at a fraction of the cost for previously prepared ampules. Essentially, these equilibrating instruments saturate blood or buffer solutions with precise amounts of single or mixed quality control gases (oxygen and/or carbon dioxide). The samples thus prepared are checked with automatic blood gas analysis systems. If the analyzer displays the predicted values for the sample, proper calibration has been verified.
U.S. Pat. No. 3,127,254 issued Mar. 31, 1964 contains a discussion of early prior art apparatus for equilibrating liquid and gas for providing quality control solutions. It is particularly directed towards an equilibration method as an alternative to the bubble type tonometers available at that time.
U.S. Pat. No. 4,256,461 issued from an application filed May 17, 1979 discloses a more recent method and apparatus for gas-liquid equilibration wherein the tonometry is carried out in a portable syringe structure utilizing a double chamber. This prior patent is significant in that it teaches the use of a heat block for providing a controlled environment for the diffusion tube wherein the equilibration is taking place. In this respect it is to be understood that proper partial pressures of the gas and liquid or blood sample can only be realized by providing a controlled temperature-pressure environment. The patentee not only teaches the use of a heat block for the diffusion tubes but shows that more than one diffusion tube can be incorporated in a single heat block thereby permitting multiple samples to be equilibrated simultaneously in a common controlled environment.
U.S. Pat. No. 4,251,483 filed Oct. 9, 1979 teaches a specific multiple independent path bubble type equilibrating apparatus or tonometer. In this particular instrument, three equilibrating operations can be carried out simultaneously in a single identical environment which, in the illustrative examples set forth, constitutes a water bath chamber incorporating the three diffusion tubes. For proper control, the usual humidifiers for providing moisture in the gas and thereby avoiding drying out of samples are incorporated in the single environment as well as the various flexible tubing interconnecting the humidifiers with the diffusion tubes. In addition, an important feature of this latter mentioned patent is the fact that the diffusion tubes incorporate a specially designed "fret" or porous member for breaking up the incoming gas into tiny bubbles, the principal characteristic being that there is provided an annular space about the member and the lower walls of the diffusion tube.
While the foregoing described equilibrating instruments or tonometers function well, it is not possible to readily clean these instruments without having to effect a substantial dismantling of the various components. For example, many times the diffusion tubes will become contaminated as well as some of the interconnected plastic tubing. Since it is not possible to easily separate these components from the remaining structure particularly when the same are enclosed in a common uniform environment, the entire instrument is simply disposed of and a new one used. Moreover, many of the presently available instruments require auxiliary controls and the like for operating the same; for example, a means for controlling the gas flow rate or even simply turning on and off the gas. These operations must normally be carried out at the gas source such as a compressed tank of gas and can result in some inconvenience in the preparation of a quality control solution.
Still another problem that can arise with presently available instruments involves those types wherein a side arm is provided on the diffusion tube to permit withdrawal of a sample after equilibration has been completed. By using such a side arm arrangement, it is indeed possible to select a sample fairly close to the portion of the solution wherein it can be assured equilibration has been completed. Such would have an advantage over simply attempting to withdraw a sample from the top of the diffusion tube. On the other hand, if the diffusion tube has to be replaced, the entire side arm mechanism must be replaced along with it. Provision of such a side arm which is also in at least part of the controlled environment makes it very difficult to provide any type of replaceable diffusion tube.